Light Curtain Systems Provide Efficient Safety Solutions

The need to improve the manufacturing process and increase work-place safety may often seem at odds with each other. Companies can sometimes view safety devices as inhibiting production. But, with the advent of new safety technologies, there are more choices than ever before, especially when it comes to safeguarding power press machines.

So what is driving the need for better safety technology for power presses and other machines for metal forming and bending? There are several trends to consider. A greater demand to incorporate lean manufacturing principles, integrate more safety solutions into machines, and combat labor shortages all play a factor.

While the idea of improving manufacturing is not new, the increased use of lean manufacturing principles has made an impact on the technologies that are developed to safeguard machines and employees. According to the ANSI Technical Report B11.TR7-2007, “More and more companies of all kinds and sizes have introduced lean manufacturing into their operations…” As a result, safety component manufacturers are looking at ways to design their safety offering to better meet the needs of lean concepts.

For example, a new light curtain developed by Minneapolis-based SICK, Inc. (Minneapolis, MN), uses DIP switches for configuration rather than a time consuming software program on a PC, saving start-up time on the power press machine. The light curtain also offers other time saving features, such as an integrated laser and bar graph alignment system and troubleshooting diagnostics right on the device so the worker does not have to waste time searching for the operations manual in the event of an error. These features were all designed based on customer feedback with lean manufacturing principles in mind.

Injuries from press machines are also another culprit that can increase downtime. Because of frequent operator involvement, these machines can represent a significant safety risk if not safeguarded properly. According to the Occupational Safety and Health Administration (OSHA), “Forty-nine percent of the injuries from mechanical power presses resulted in an amputation.” Using proper safeguards on power press machines lowers the risk of downtime due to injuries or the cost and time it takes to retrain an employee to fill in for the injured worker.

While a company’s goal may be to cut waste, boost quality and reduce costs, there are also benefits from improved safety. As a result, safety component manufacturers are working more with machine builders to integrate safety solutions right on the machine. Solutions range from interlocks… to highly automated, machine-specific solutions, such as a camera-based safety system designed for press brake machines. Often, several types of safety solutions are used in combination and built onto the machine.

If safety is taken into consideration at the onset of machine design, then the safety solution can be designed to optimize production rather than slow it down. The ANSI Technical Report B11.TR7-2007 provides a good example, “…interlocked guards can be designed to open quickly providing good access and easy replacement for necessary changeover work. If the need for quick release is not considered early, a fixed guard might be used, greatly slowing the changeover task.”

Labor shortages also factor into making safety products more user friendly. As experienced forming and fabricating workers retire, there are not enough skilled workers to replace them. As a result, safety systems manufacturers have responded by designing products that are more automated, simpler to install and easier to use. A line of safety controllers, for example, can now be programmed with a screwdriver rather than a PC.

Trends in Safety Solutions by Application

Safety integrators now look at safety as a system rather than individual components. Some customers also take this approach, but many smaller metal fabricating companies do not. Looking at safety from a system approach translates into a more efficient operation overall. In the US, customers are doing more custom jobs, so their safety system has to be more flexible to meet frequent part changeovers. The solutions that they buy must meet those needs for flexibility and be easy enough to implement. This is due in part to the shortage of experienced workers. As a result, the solutions have to be more automated and allow for less interaction with the machine, so the operator can concentrate on getting the orders completed and out the door quickly.

Mechanical and Hydraulic Presses

Safeguarding of Mechanical and Hydraulic Presses are covered under ANSI B11.1 and B11.2 respectively. They cover what is necessary and acceptable to properly safeguard these machines.

One of the points of emphasis is point-of-operation guarding. Safeguarding at the location in a machine where material is positioned and processed is known as point-of-operation safeguarding. The goal of point-of-operation safeguarding is to prevent the operator from being exposed to a hazardous motion when the machine performs the process on the material.

Considerations for using a safety light curtain, or any other safeguarding device, when considering point-of-operation safeguarding, are outlined in ANSI B11.19. The corresponding explanation states: “A presence sensing device shall prevent the operator or others from reasonably reaching over, around, under or through the sensing field into the hazardous area.” Auxiliary safeguarding may be required in conjunction with the safeguarding device to accomplish this requirement.

Safeguarding the front of the press is generally performed using safety-rated devices such as hard guarding, palm stations or light curtains that also incorporate a control system that satisfies the requirements of control reliability. To prevent access to the hazardous motion of a press, machine safeguards must be installed to account for minimum safety distance requirements. This minimum safety distance is based on the overall response time of the machine safeguards and the stop time of the machine itself. Finer resolution light curtains (≤14mm resolution ? finger detection) can be utilized to minimize this minimum safety distance. Other resolutions are available, but must account for increased depth of penetration factors that lead to installations further away from the point of operation.

Gary Pappas, president of Tower Machinery, a machine tools integrator, commented “Certainly hard guarding is still used, but the most flexible method remains light curtains.” Pappas also stated, “For hard guarding to be effective, any hinged guard must be interlocked to the press. Additionally, fixed guards must require a special tool for their removal.

Before you can add any light curtains, there are a number of things you need first,” he continued. Among the most common items needing correction on a press include upgrading the control to be control reliable and making sure you have a modern dual solenoid back checking air valve. Many times when a customer calls to have light curtains installed on a press, these and other items need to be addressed first,” he concluded.

Rather than selling a customer more than what they need, today, there are many light curtain options on the market to meet specific customer needs. Safety light curtains can be ordered in a variety of resolutions, protective heights and variants from simple beam break functionality to advanced fixed, floating and dynamic blanking for implementing complex and multi-mode safeguarding applications that allow the machine to be run more efficiently.

Daisy chaining is one method of safeguarding that is becoming more popular, noted Pappas. “I have seen more people using multiple sets of light curtains on power presses when blanking is required, instead of mirrors with light curtains. This ‘daisy chain’ method offers certain advantages,” he says.

“If you have a conveyor on the exit side of the press you typically would blank the profile of the conveyor to allow it to extend beyond the light curtains. If you are using mirrors with the light curtains, the area that has been blanked out for the conveyor on the exit side of the press is also blanked out in the front of the press, when there is no obstruction in the front of the press. This could leave the hazard exposed if the blanked window isn’t taken into consideration when calculating the safety distance,” he concluded.

Daisy chaining light curtains minimizes wiring when multiple sets are required for a single machine. This reduces the cost for multiple safety relays, simplifies the installation, and reduces the time required for integration. There is also a simple teach function where you can teach the light curtains to blank a different area for each of the three sets of daisy chained light curtains.

Hydraulic Press Brakes

There are a number of regulations and standards that apply to the hydraulic press brake, in general press brakes require point of operation safeguarding between the hazardous pinch point created by the punch and die. There is also a requirement for protection at the back of the machine.

Press brakes are used to bend metal into various shapes. The ram of the machine, which includes a punch or tool for the specific job, descends downward toward the material that is held on the die by the operator. A hazardous condition or pinch point exists when the punch and die meet. Serious injury can occur if a person is caught between the punch and the material on the top of the die.

The back of the press brake is typically open, which would allow a person access to the dangerous movements and pinch points of the other parts of the press brake such as the backguage and hydraulic system.

Camera-based systems for safeguarding press brakes are one of the latest trends. The V4000 Press Brake Safety System from SICK is an all inclusive sensor and evaluation system, consisting of a sender and a receiver mounted on the upper beam of the press, which safeguards the punch during the fast downward movement. It creates a safety volume below the punch line and its Output Signal Switching Devices (OSSDs) provide a signal to the press controller to stop the closing movement of the press as soon as an object (such as a hand or finger) is detected.

This type of safeguarding system helps with productivity versus light curtain because it handles a wide variety of bending applications and allows the operator to get closer to the machine. “The SICK V4000 is the only camera based system currently on the market using pixels to define a safety zone. This allows the operator to form small parts very close to the point of operation on hydraulic press brakes, concluded Pappas.

There are several options for safeguarding the back of the press brake. Light curtains are frequently used. The access protection on the rear of the press brake is provided using a host/guest system comprising a vertically mounted and a horizontally arranged light curtain as point-of-operation guarding. Entry into the hazardous area stops the dangerous movements of the press. Another option is the use of hard guarding with a safety interlock to stop machine movement with the door is opened.

Conclusion

Safeguarding can impede or enhance productivity, depending on a number of things, including the safety solutions used, production requirements, machine design, the work cell, and other factors. Therefore, it is key to take a systems approach to safety and rely on a knowledgeable integrator to suggest the best solution for your particular needs. While there are many ways to safeguard machines, new safety technologies are often developed based on the need to streamline and automate processes, integrate solutions and make safety devices easier to use.

www.sick.com